This invention relates to a process and apparatus for the manufacture of thin-walled articles from a powdered thermoplastic and more particularly to the manufacture of such articles by use of a re-claiming and make-up powder supply and associated method and means for uniform distribution of thermoplastic powder against a heated mold surface which causes the powder to become fused.
Process and apparatus for molding hollow articles from powder thermoplastic material is set forth in U.S. Pat. Nos. 3,301,925 issued Jan. 31, 1967 to Engel and 3,492,307 issued Jan. 27, 1970 to Hutchinson. In the '307 patent interlocked mold and charge box components are rotated to distribute thermoplastic powder into the mold. In the '925 patent a stand-pipe spray system directs thermoplastic material against a heated mold surface and excess material is recycled by use of a gravity feed funnel. Other distribution and recycle systems for molding hollow articles from thermoplastic material are set forth in U.S. Pat. Nos. 3,315,016 and 3,418,694, respectively, issued Apr. 18, 1967 to Wersosky et al. and Strauss. The distribution of plastic is suitable for the mold configurations and product to be formed in these patents.
However, in order to produce optimum build-up of thermoplastic powder on heated walls of a mold surface such systems tend to expose certain regions of the mold to greater quantities of the powder fill and as a result such surfaces of the mold will have a thicker build-up of plastic formed thereon.